My short summary of Alasdair John Milbank on human rights:
Prior to modernity, “rights” (Latin iura) were seen as the participation of persons in relationships of mutual, free associations in something objective. But with the advent of liberal political thought, rights become absolutely grounded in the subjective self in isolation from others. American political precedent is built upon these modern assumptions. Hence, “gay marriage” is perfectly rational in an American context which is built on the foundations of modern, liberal political thought.
I would add: if one is not prepared to challenge the foundations of American political theory (including the US Constitution), then one should not complain about gay civil “marriage.”
Two caveats here:
1. I do not mean to imply that the meaning of the word “marriage” (which is a sacrament of the Church) can be redefined. Indeed, I wonder why secular people even care about something called “marriage,” if not for financial reasons based in the tax code of the US. Thus, the church ought to disentangle itself from the state when it comes to marriage.
2. None of the above discussion applies to decisions within the Church with respect to issues around “homosexuality.”